1. Field of the Invention
This invention relates to gas springs and, more specifically, to new and improved structure for providing enhanced damping of the rate of movement of the piston rod outward of the cylinder as the cylinder approaches its outermost position. The invention has particular application to uses in which the gas spring is mounted in the rod-down orientation when the piston rod is fully retracted and moves to the rod-up orientation as the piston rod travels outward of the cylinder.
2. The Prior Art
Gas springs having provision for damping the rate of outward movement of the piston rod as the rod nears its outermost position are known in the art. Such a gas spring is disclosed, for example, in U.S. Pat. No. 3,963,227. In that patent, a cup-shaped damping cylinder is provided at the inner end of the piston rod member and an annular damping piston is fixed to the cylinder in surrounding relation to the piston rod. As the piston rod nears the outermost position, the damping cylinder carried by the piston rod telescopes over the fixed damping piston to slow the rate of outward movement. Although this prior art structure is generally useful, it is comparatively complicated in design and expensive. Also, it affords only one further stage of damping, whereas in certain applications a plurality of additional damping rate-stages is needed or desirable.